5. Potentiometer

The potentiometer is a variable resistor.

Turn it one way to reduce the resistance. Turn it the other way to increase it.

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5.1. Model

1. Place the potentiometer.

2. Connect with the jumper wires.

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5.2. Read analog

To read the value of the potentiometer use pin2.read_analog.

The code below reads the value and displays it.

Try turning it from side to side to see the effect.

from microbit import *

while True:
    potval = pin2.read_analog()
    display.scroll(potval, delay=80)
    sleep(20)

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Tasks

1. Modify the code to use a function, display_potentiometer_value, that reads the potentiometer and scrolls its value. Include a default parameter for the pin.

Q1

Modify the code to use a function, display_potentiometer_value, that reads the potentiometer and scrolls its value. Include a default parameter for the pin.

from microbit import *


def display_potentiometer_value(pin=pin2):
    potval = pin.read_analog()
    display.scroll(potval, delay=80)


while True:
    display_potentiometer_value()
    sleep(20)

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5.3. Advanced: Power meter simulation

The code below takes an analog value from the potentiometer and displays it on the microbit LEDs.

See the custom images lesson for more on display.set_pixel.

The maximum potentiometer reading is 1023, so this can be treated as 1000 for simplicity.

This gives 5 levels in steps of 200.

Each row step of 200 can be divided into 10 steps of brightness from 0 to 9.

3 variables are used for each section of the display: yclearlist for the blank rows, ylist for the full brightness rows and yval for the row in between that is of partial brightness.

yclearlist has the rows which are at brightness of 0.

ylist has the rows which are at brightness of 9.

yval is the row with variable brightness.

Each of these variables is first checked to see if it is None before setting the pixels it controls.

def display_level(level):
    xlist = [0, 1, 2, 3, 4]

    # display
    val = int((level % 200) * 9 / 200)
    if level < 200:
        yval = 4
        ylist = None
        yclearlist = [0, 1, 2, 3]
    elif level < 400:
        yval = 3
        ylist = [4]
        yclearlist = [0, 1, 2]
    elif level < 600:
        yval = 2
        ylist = [3, 4]
        yclearlist = [0, 1]
    elif level < 800:
        yval = 1
        ylist = [2, 3, 4]
        yclearlist = [0]
    elif level < 1000:
        yval = 0
        ylist = [1, 2, 3, 4]
        yclearlist = None
    else:
        yval = None
        ylist = [0, 1, 2, 3, 4]
        yclearlist = None

    for x in xlist:
        if yval is not None:
            display.set_pixel(x, yval, val)
        if ylist is not None:
            for y in ylist:
                display.set_pixel(x, y, 9)
        if yclearlist is not None:
            for y in yclearlist:
                display.set_pixel(x, y, 0)

Try the full code.

from microbit import *


def display_level(level):
    xlist = [0, 1, 2, 3, 4]

    # display
    val = int((level % 200) * 9 / 200)
    if level < 200:
        yval = 4
        ylist = None
        yclearlist = [0, 1, 2, 3]
    elif level < 400:
        yval = 3
        ylist = [4]
        yclearlist = [0, 1, 2]
    elif level < 600:
        yval = 2
        ylist = [3, 4]
        yclearlist = [0, 1]
    elif level < 800:
        yval = 1
        ylist = [2, 3, 4]
        yclearlist = [0]
    elif level < 1000:
        yval = 0
        ylist = [1, 2, 3, 4]
        yclearlist = None
    else:
        yval = None
        ylist = [0, 1, 2, 3, 4]
        yclearlist = None

    for x in xlist:
        if yval is not None:
            display.set_pixel(x, yval, val)
        if ylist is not None:
            for y in ylist:
                display.set_pixel(x, y, 9)
        if yclearlist is not None:
            for y in yclearlist:
                display.set_pixel(x, y, 0)


def display_potentiometer_level(pin=pin2):
    potval = pin.read_analog()
    display_level(potval)


while True:
    display_potentiometer_level()
    sleep(20)